Free piston engine



Feb. 16, 1960 G. H. MILLAR FREE EIs'roN ENGINE Filed Dec. 17, 1956 ,4 JV l 27 m FIG.1.

22 is r [ll/d4 FIG. 2

ATTORNEYS 2,925,013 W FREE PISTON ENGINE Application December 17, 1956, Serial No. 628,737

3 Claims. (Cl. 123-46) This invention relates to free piston engines and is more particularly concerned with an outboard compression type engine.

In adapting the free piston engine to automotive use, it has been found that an inboard compression unit is undesirably bulky. This stems from the fact that the engine requires a large air box or plenum which receives the air from the compressor and stores it for one half cycle prior to utilization by the engine. To avoid this difficulty, attempts'have been made to employ an outboard compression engine which discharges compressed air from the compressor sectionat essentially the same time in the operating cycle that scavenging of the engine cylinder takes place thereby allowing the use of a smaller air box. This type of engine requires additional ducting to deliver the compressed air to the engine cylinder which enlarges the radial dimension of the engine because of the physical arrangement of the compressor cylinder head and the engine cylinder of the engine.

It is therefore an object of this invention to provide an outboard compression type freepiston engine which does not require external manifolding around the compressor cylinder. This is accomplished by conducting the air directly through passageways in a piston of novel construction into the engine cylinder.

My invention can better be appreciated by reference to the drawings which show somewhat schematically my invention and in which:

Figure l is a section of my invention with the pistons in the inboard position, i

Figure 2 is similar to Figure 1:but rotated 90 about its longitudinal axis and shows the pistonsin the outboard position.

As indicated in Figure l, the engine comprises a generally cylindrical housing 11 having chambers 12 and 13 at opposite ends, a combustion cylinder 14 centrally located between these chambers, and a pair of opposed power pistons 15 and 16 which operate within cylinder 14. At the outboard end of these pistons are a pair of enlarged compressor pistons 17 and 18 which are integral with pistons 15 and 16 or are rigidly attached to them and which operate within chambers 12 and 13 thereby dividing it into outboard compressor portions 19 and 20 and inboard portions 21 and 22. Ports 23 and 24 provide the air intake to chambers 13 and 12 respectively. Communicating with the compressor sections 19 and 20 are longitudinal bores in the pistons such as that shown at 26 in the right hand piston. The bore corresponding to bore 26 is not visible in the left hand piston, however, it is located within the piston at the left exactly as bore 26 is located within its piston. These bores are connected to the enlarged piston ports 27 and 28 via transverse bores 29 and 30. A pair of compressed air inlet or scavenge ports 31 displaced'approximately 90 from ports 27 in the piston are located in the left portion of cylinder 14. Manifolded delivery ports 32 in the right hand portion of the cylinder are located'slightly closer to the inner dead point of the cylinder than ports 31 a d States Patent Patented Feb. 16,4960

to provide uniflow scavenging. Air passage intake ports 33 and 34 in opposite ends of cylinder 14 are radially aligned with the ports 27 and 28 in the piston so that these cylinder ports register with their respective openings in the piston at the proper time in the operational sequence of the engine. An annular passage 35 formed between the combustion cylinder 14 and the cylindrical housing 11 provides a connection between the interior of the combustion cylinder and compressor chambers 19 and 20 via ports 33 and 34 and inlet port 31.

It is to be understood that many parts of the system (e.g., the piston synchronism mechanism and the fuel system) have been omitted in the above description in order that my invention will be more readily appreciated. However, the parts omitted are conventional and well known and'may easily be supplied by those conversant with this art.

The operation of my device may be best understood by following the sequence in views 1 and 2.

With the pistons at the inner dead point as in Figure 1, inlet ports 23 and 24 are open to the atmosphere allowing the pressure in the compressor sections 19 and20 to reach ambient conditions. As the piston begins to move outboard, ports 23 and 24 are effectively closed to the compressor sections by the movement of the compressor pistons beyond these ports and the pressure in the compressor section begins to rise since ports 27 and 28 in the power piston remain sealed by the cylinder 14. As the pistons continue in their outboard movement they pass the ports 32 and open them allowing the hot engine gases formed by the prior compression ignition of the fuel in the central portion of the combustion cylinder to commence to blow down through suitable ducting .25 to the turbine inlet (not shown). As the pistons near the outboard position, ports 27 and 28 in the pistons register with ports 33 and 34 and ports 31 are open since the piston clears these ports almost simultaneously with the opening of ports 32. The air which has been compressed by the action of the compressor piston flows through the longitudinal bores in the respective pistons, through the transverse bores 29 and 30 to ports 27 and 28 and into passageway 35 via ports 33 and 34. Theair then flows through port 31 into the central portion of the cylinder and sweeps the remaining combustion gases out through exhaust 32. After this scavenging process is complete the pistons begin to return inward, the ports 33 and 34 in the combustion cylinder are closed by the respective pistons, then ports 31 are in turn closed and almost immediately thereafter ports 32 are closed and the compression cycle begins. When the pistons approach the inner dead point, a charge of fuel is injected into the combustion cylinder by a suitable nozzle (not shown). The compressor inlet ports 23 and 24 then communicate with their respective compressor sections 19 and 20, the fuel charge is ignited by compression, and the cycle is repeated.

If it is desired, valves may replace ports 23 and 24 to increase the volumetric eificiency of the compressor. However, the lower volumetric efficiency of the ported compressor is not a great disadvantage because the large clearance in the compressor is used to store the energy which may be used to return the pistons inboard to further compress the air and fuel mixture within the power cylinder.

Having described my invention in detail it is apparent to anyone skilled in the art that it is susceptible of many embodiments and modifications without departing from the spirit of the invention. Therefore, the examples given above should not be construed as limiting my invention in any manner and the scope of my invention is to be defined only by the appended claims.

I claim:

1. A free piston engine comprising, a combustion cylinder, a combined outboard compressor and bounce chamber located at each end of said combustion cylinder, a pair of opposed power pistons positioned in said combustion cylinder, each of said power pistons having a combined compressor and bounce piston attached thereto, one of said combined compressor and bounce pistons being positioned in one of said combined compressor and bounce chambers, the other of said combined compressor and bounce pistons being positioned in the other of said combined compressor and bounce chambers, said combined compressor and bounce pistons compressing air in the combined compressor and bounce chambers on the combustion stroke of said power pistons, a casing surrounding said combustion cylinder in spaced relation thereto to form an airpassage around said combustion cylinder, a scavenge port positioned in the combustion cylinder adjacent one outboard end thereof, a delivery port positioned in the combustion cylinder adjacent the other outboard end thereof, one of said power pistons uncovering said scavenge port during the latter portion of the combustion stroke of said power piston and during the initial portion of the compression stroke of said power piston so that the air passage communicates with the interior of said combustion cylinder, the other of said power pistons uncovering the delivery port during the latter portion of the combustion stroke and during the initial portion of the compression stroke of said other power piston, fluid passage means connecting said 'air passage with the combined compressor and bounce chambers during the latter portion of each combustion stroke and the initial portion of each compression stroke of the power pistons, said passage means comprising a longitudinal bore in each of the combined compressor and bounce pistons, said longitudinal bore extending into the power pistons, a transverse bore positioned in each of the power pistons communicating with the longitudinal bore, and ports positioned in opposite ends of said combustion cylinder, a portion of the compressed air in said combined compressor and bounce chambers flowing through the longitudinal bores in said combined compressor and bounce pistons and said power pistons, through the transverse bores in said power pistons, through the ports positioned in the opposite ends of said combustion cylinder, through said air passage, through said scavenge port to scavenge said combustion cylinder by blowing products of combustion out of said combustion cylinder through said delivery port, the remainder of'the compressed air in said combined compressor and bounce chambers acting on said combined compressor and bounce pistons for moving said power pistons and said combined compressor and bounce pistons inwardly on the compression stroke of the engine.

2. A free piston engine comprising, a combustion cylinder, a combined outboard compressor and bounce chamber located at each end of said combustion cylinder,

a pair of opposed power pistons positioned in said combustion cylinder, each of said power pistons having a combined compressor and bounce piston attached thereto, one of said combined compressor and bounce pistons being positioned in one of said combined compressor and bounce chambers, and the other of said combined compressor and bounce pistons being positioned in the other of said combined compressor and bounce chambers, said combined compressor and bounce pistons compressing air in the combined compressor and bounce chambers on the combustion stroke of said power pistons, an air passage positioned around said combustion cylinder, at scavenge port positioned in the combustion cylinder adjacent one outboard end thereof, a delivery port positioned in the combustion cylinder adjacent the other outboard end thereof, one of said power pistons uncovering the scavenge port during the latter portion of'the combustion stroke of said power piston and during the initial portion of the compression stroke of said power piston, the other of said power pistons uncovering the delivery port during the latter portion of the combustion stroke and during the initial portion of the compression stroke of said other power piston, fluid passage means connecting said air passage with the combined compressor and bounce chambers during the latter portion of each combustion stroke and during the initial portion of each compression stroke of the power pistons, said passage means comprising fluid conduit means positioned in each combined compressor and bounce piston and in each power piston, and a port positioned at each outboard end of said combustion cylinder, a part of the compressed air in said combined compressor and bounce chambers flowing through the fluid conduits in the combined compressor and bounce pistons and the power pistons, through the ports positioned in the combustion cylinder, through the air passage, through the scavenge port, and into the combustion cylinder to scavenge the engine by blowing products of combustion out of the combustion cylinder through said delivery port, the remainder of the compressed air in said combined compressor and bounce chambers acting on the combined compressor and bounce pistons for moving said power pistons and said combined compressor and bounce pistons inwardly on the compression stroke of the engine.

3. A free piston engine having a combined outboard compressor and bounce chamber comprising, a combustion cylinder, a power piston operable in said combustion cylinder, said combined compressor and bounce chamber comprising a cylinder attached to said combustion cylinder and a combined compressor and bounce piston positioned therein, said combined compressor and bounce piston being connected to said power piston, said combined compressor and bounce piston compressing air in the combined compressor and bounce chamber on the combustion stroke of said power piston, said combustion cylinder having a scavenge port positioned therein, an air passage positioned around said combustion cylinder and communicatingwith the interior of said combustion cylinder via said scavenge port during the latter portion of the combustion stroke of said power piston and during the initial portion of the compression stroke of the power piston, passage means connecting said air passage with the outboard portion of said combined compressor and bounce chamber during the latter portion of each combustion stroke and during the initial portion of each compression stroke of the power. piston, said passage means comprising fluid conduit means positioned in the combined compressor and bounce piston and the power piston, and a port positioned at the outboard edge of said combustion cylinder, a portion of the compressed air in said combined compressor and bounce chamber flowing through the fluid conduits in said combined compressor and bounce piston and the power piston, through the port positioned in said combustion cylinder, through the air passage and into the combustion cylinder via the scavenge port to scavenge the engine, the remainder of the compressed air in said combined compressor and bounce chamber acting on the combined compressor and bounce piston for moving said power piston and said combined compressor and bounce piston inwardly on the compression strokeof the engine.

References Cited in the file of this patent UNITED STATES PATENTS 1,215,865 Rishel Feb. 13, 1917 1,354,667 Lawler Oct. 5, 1920 1,461,948 Stosik -2 July 17, 1923 2,101,412 Pescara Dec. 7, 1937 2,182,063 Steiner Dec. 5, 1939 2,227,853 Turner Jan. 7, 1941 2,435,232 Morain Feb. 3, 1948 FOREIGN PATENTS 568,382 Great Britain Apr. 3, 1945 

